Role of Indole-3-Acetic Acid in NAFLD Amelioration After Sleeve Gastrectomy

Background This study aimed to investigate the weight-independent mechanism of sleeve gastrectomy on the relief of nonalcoholic fatty liver disease (NAFLD). Methods A total of 58 obese patients who had undergone sleeve gastrostomy (SG) were recruited. Plasma levels of indole-3-acetic acid (I3A), a metabolite from gut microbiota before and after SG were investigated. In addition, we had 78 C57BL/6J mice included in the study. High-fat diet (HFD) was used to induce obesity in mice. Sleeve gastrectomy (SG) was then performed. The liver of the mice was analyzed by HE and oil red staining to study lipid accumulation. Fluorescence-activated cell sorting (FACS) analysis was performed to study the phenotype of macrophages in the liver. The levels of I3A in serum, stool, and liver were tested by ELISA. Macrophages and hepatocytes were cultured in vitro and stimulated with I3A to study the effects on differentiation and proliferation/apoptosis. Results In human samples, I3A increased after SG and plasma I3A levels were positively correlated with liver CT values and negatively correlated with liver fat attenuation. In mice models, after surgery, the percentage of M2 macrophages significantly increased in the liver. Both oral gavage and in vitro stimulation of I3A could promote M2 differentiation and did not significantly affect the state of hepatocytes. Conclusions This study suggested that increased I3A from the intestine after SG could reduce the M1/M2 ratio in the liver and thus promote relief of NAFLD in obese individuals. Graphical Abstract